Currently, the communications and networking industries utilize optical fibers that are single mode fibers, very small in cross-section, and typically have a fairly narrow acceptance angle within which light entering the fiber must fall to promote efficient propagation of the light along the fiber. Therefore, optical switches which accept light from an input optical fiber, and selectively couples that light to any of a plurality of output optical fibers must transfer that light with precise alignment. The alignment requirements of modern single mode optical fibers are particularly stringent, as their core diameters are typically as small as around 8 micrometers.
In electromechanical 2×2 optical switches, the switching operation is typically effected by the movement of a double-side mirror to couple input light into the ends of each of two output optical fibers, with an optical lens utilized to expand and collimate light from the fibers. To form two optical paths in a 2×2 optical switch, the collimated light beam from the input fibers must accurately align with output collimators to avoid excessive loss of the signal therebetween. This alignment requires a two angle/two position matching operation to occur between input collimators and output collimators.
In addition, in a 2×2 optical switch based on a double-side mirror, each side of the mirror provides for one optical path. This requires additional accuracy to ensure that the optical paths between the two sides of the mirror are parallel to one another. It tremendously increases the cost and complexity for this special mirror and makes it inherently very difficulty to manufacture such a 2×2 optical switch. Another disadvantage of this kind of 2×2 optical switch is the need for at least two collimating lenses, which adds to the bulkiness of the overall package.
U.S. Pat. No. 5,742,712 describes a 2×2 optical switch arrangement in which the optical fibers are housed in a sleeve, the sleeve having a central aperture, which can be circular or square, in which the four fibers of the 2×2 switch arrangement are housed. The fibers are maintained in close proximity to one another, the optical axis of each fiber being at a substantially constant distance from the longitudinal axis of the sleeve itself. Hence, the architecture provides for a somewhat bulky arrangement.
In addition, if this type of architecture were expanded to accommodate a 4×4 switch arrangement, the addition of further fibers would add significantly to the bulkiness of the device, since the additional fibers would need to be accommodated such that their cores were also constant distance from the longitudinal axis of the sleeve, thereby adding to the radial dimension of the sleeve.